A memory cell has a memory transistor, which is provided with a gate electrode at a top side of a semiconductor body or a semiconductor layer. The gate electrode is arranged between a source region and a drain region, which are formed in the semiconductor material. The gate electrode is isolated from the semiconductor material by a dielectric material. In the case of a charge trapping memory cell, in particular a SONOS cell or NROM cell, a layer sequence comprising a storage layer provided for trapping charge carriers at source and drain between boundary layers is present at least between the source region and the gate electrode and between the drain region and the gate electrode. The material of the boundary layers has a higher energy band gap than the material of the storage layer, so that the charge carriers trapped in the storage layer between the boundary layers remain localized there.
A nitride is preferably taken into consideration as material for the storage layer. An oxide is principally suitable as the surrounding material. In the case of a memory cell in the material system of silicon, the memory cell in this example is silicon nitride with an energy band gap of about 5 eV, and the surrounding boundary layers are silicon oxide with an energy band gap of about 9 eV. The storage layer may be a different material with a smaller energy band gap than that of the boundary layers, the difference between the energy band gaps being intended to be as large as possible for good electrical confinement of the charge carriers. In conjunction with silicon oxide, it is less possible to use e.g., tantalum oxide, hafnium silicate, titanium oxide (in the case of stoichiometric composition TiO2), zirconium oxide (in the case of stoichiometric composition ZrO2), aluminum oxide (in the case of stoichiometric composition Al2O3) or intrinsically conducting (undoped) silicon as material of the storage layer. Silicon nitride has a relative permittivity of about 7.9. The use of an alternative material with a higher relative permittivity (e.g. ≈15 . . . 18) permits a reduction of the oxide-equivalent overall thickness of the layer stack provided for storage and is therefore advantageous.